Silver halide emulsions containing antibronzing agents



United States Patent Olfice 3,409,437 SILVER HALIDE EMULSIONS CONTAINING ANTIBRONZING AGENTS Ralph A. Copeland, Chenango Bridge, and Fritz Dersch and Charles A. Clark, Binghamton, N.Y., assignors to GAF Corporation, a corporation of Delaware No Drawing. Filed Feb. 26, 1965, Ser. No. 435,710

9 Claims. (Cl. 9695) ABSTRACT OF THE DISCLOSURE Light-sensitive photographic element and silver halide emulsion therefor, containing as an antibronzing agent, at least 0.5 gram per mole of silver halide of a diphenyldisulfidedicarboxylic acid in which the disulfide bridge occupies the position meta or para to the carboxyl group in each of the benzene rings.

This invention relates to light-sensitive silver halide emulsions containing either diphenyldisulfide-3,3'-dicarboxylic acid or diphenyldisulfide-4,4'-dicarboxylic acid antibronzing agents. More particularly, this invention relates to light-sensitive gelatino silver halide emulsions containing diphenyldisulfide-3,3-dicarboxylic acid or diphenyldisulfide-4,4-dicarboxylic acid antibronzing agents.

It is well known that silver images produced by exposure and processing of silver halide emulsions often tend to lose their blackness and take on an undesirable brownish shade. Accompanying this undesirable discoloration, which is called bronzing, there is also a shift and decrease of intensity of the image tone during drying. This image degradation is frequently emphasized in the final ferrotyping stage. A number of suitable antibronzing agents have been described in the prior art. However many of these compounds have undesirable side-effects such as reducing the sensitivity of the silver halide emulsions, or by accumulating in the processing solutions changing the development rate of subsequently processed light-sensitive emulsions. For example, when mercapto containing antibronzing agents are used in the necessary concentration, the silver halide emulsion speed is reduced two or three stops.

The object of this invention is to provide suitable antibronzing agents which do not reduce the sensitivity of silver halide emulsions or tend to dissolve in the processing solutions changing the development rate of developing solutions.

We have now found that diphenyldisulfide-3,3'-dicarboxylic acid and diphenyldisulfide-4,4'-dicarboxylic acid, are excellent antibronzing agents having all of the above desirable properties. Of the two, the diphenyldisulfide- 3,3dicarboxylic acid is considered to be more effective. Surprisingly, the diphenyldisulfide-2,2'-dicarboxylic acid is unsuitable for use in our invention. This is apparently due to the higher solubility of the diphenyldisulfide-2,2- dicarboxylic acid whch makes it virtually impossible to incorporate a sufficient concentration of antibronzing agent into the silver halide emulsion.

As pointed out in commonly assigned application, Ser. No. 281,054, filed May 16, 1963, diphenyldisulfide-3,3- dicarboxylic acid, diphenyldisulfide-2,2'-dicarboxylic acid, diphenyldisulfide-4,4'-dicarboxylic acid are all useful as antifogging agents. For antifogging use the diphenyldisulfidedicarboxylic acids are used in a concentration of .02 to 20 mg. per 0.6 gram moles of silver halide (i.e., 0.33 to 33.3 mg. per mole of silver halide). For use in our invention the diphenyldisulfide-3,3-dicarboxylic acid and diphenyldisulfide-4,4'-dicarboxylic acid must be used in substantially greater concentrations, i.e., in the range of 0.5

3,409,437 Patented Nov. 5, 1 9 68 to 5 grams per mole of silver halide. Even at concentrations, which are markedly greater than that necessary for effective antifogging purposes, no noticeable antibronzing effect is noticed. For example, at a concentration of 0.2 g. per mole of silver halide, the diphenyldisulfidedicarboxylic acids of our invention yield little, if any, improvement over the same emulsions containing no diphenyldisulfide-3,3'-dicarboxylic acid. In general best results have been obtained using concentrations of about 1 to 2 grams diphenyldisulfidedicarboxylic acids per mole of silver halide. At this concentration excellent blacks are obtained with minimal loss of emulsion sensitivity.

The antibronzing agents of our invention may be added to the emulsion at any stage during its production. Thus, they may be added as a ripening final or as a coating final. When added as a ripening final, they are added during the ripening or sensitivity-increasing stage of the emulsion-making process. Such addition may be made before, during or after the addition of a soluble silver salt to the soluble halide in the presence of a suitable colloid, such as gelatin the coloid of choice), polyvinyl alcohol, solubilized casein, albumin, etc.

When added as a coating final, the antibronzing agents of this invention are added to the emulsion just prior to coating it on a suitable support, such as paper or film, at a time when the emulsion has nearly attained its maximum sensitivity. If desired, the antibronzing agents can be added to the adjacent layer, such as an antiabrasion gelatin layer. v

The emulsion may be optically or chemically sensitized. By chemically sensitized we mean to include sulfur sensitizing, reduction sensitizing, metal sensitizing, etc. If desired polyalkylene oxides and derivatives thereof may also be added to the emulsionfAdditional colloid material, such as PVP which serves to improve the covering power of the emulsion, may be employed. Various stabfizers, such as 7-hydroxy-5-alkyl-5-triazole (2,3-a) pyrimidines or antifoggants, such as phenyl-mercaptotetrazole may be employed.

The diphenyldisulfide-3,3-dicarboxylic acid can be prepared by adding zinc dust in small portions to salts of chlorosulfonylbenzoic acid in ethanolic hydrochloric acid with adequate agitation. A more detailed method of preparing this compound is described in the aforementioned application, Ser. No. 281,054. The paraisomer is described in Beilsteins Handbuch der Organischen Chemie, vol. X, page 111.

The diphenyldisulfidedicarboxylic acids of our invention are added to the colloidal carrier either in aqueous solution, such as an alkali metal salt (potassium or sodium) or from organic solution, such as dimethyl formamide, diethyl formamide, ethanol, methanol, etc. For the purposes of this invention, it is to be understood that the term diphenyldisulfidedicarboxylic acids includes both the free acid and the water-soluble salts thereof.

The examples following are merely illustrative and should not be construed as limiting the scope of this invention.

EXAMPLE 1 A silver halide gelatin emulsion containing 60% AgCl and 40% AgBr was prepared in the conventional manner and brought up to its maximum light sensitivity. It was then readied for coating, finals were added such as sensitizing dyes and hardening agents. One g. of diphenyldisulfide-3,3'dicarboxylic acid which had been dissolved in 8 ml. of dimethyl formamide and diluted to 20 ml. with methanol was added to the above gelatin emulsion containing one mole silver halide. The emulsion was then coated on a cellulose ester film base and dried. Samples of the film thus coated were then exposed to actinic radiation and developed in a developer having the following composition:

Grams Phenidone 0.1 Hydroquinone 2.8 Sodium sulfite 12.0 Aqueous sodium carbonate 24.0 Potassium bromide 0.28 Benzotriazole 0.05 Water to make 1 liter.

EXAMPLE II A concentration series of emulsions was prepared utilizing 0.0 g., 0.05 g., 0.125 g., 0.25 g., 0.50 g. and 1.0 g. of diphenyldisulfide-4,4'-dicarboxylic acid per kilo of a silver chloro-bromide emulsion, said silver chloro-bromide emulsion containing 25 g. of silver per kilo of emulsion. Each of these emulsions was applied to a suitable cellu lose acetate strip in the conventional manner, exposed, developed with a developing solution utilized in Example I and ferrotyped on a hot drum. The prints prepared using 0.05 g. of diphenyldisulfide-4,4-dicarboxylic acid had little, if any, improvement over the emulsion prepared without any diphenyldisulfide-4,4'-dicarboxylic acid. A marked improvement in the image blackness was attained during 0.125 g. of diphenyldisulfide-4,4'-dicarboxylic acid. Best results were obtained at diphenyldisulfidedicarboxylic acids concentrations of 0.25 to 0.5 g. of diphenyldisulfide-4,4'-dicarboxylic acid per kilo of silver halide emulsion (approximately 1 to 2 grams of diphenyldisulfide 4,4 dicarboxylic acid per mole At 0.50 g. and 1.0 g. of diphenyldisulfidedicarboxylic acids per kilo of silver halide emulsion (approximately 1 to 2 grams of diphenyldisulfide-4,4'-dicarboxylic acid per mole of silver halide). The emulsion containing 0.125 and 0.25 g. per kilo results in loss in emulsion speed of /2 stop. At 0.50 g. and 1.0 g. of diphenyldisulfidedicarboxylic acids the emulsion had a slightly lower sensitivity (a loss of /1 stop).

The concentration series utilized was prepared in the manner described in Example I. The diphenyldisulfide-4, 4-dicarboxylic acid was put in solution by suspending 0.5 g. of said compound in 100 ml. of methanol and adding sufiicient lN NaOH until the diphenyldisulfidedicarboxylic acids dissolved.

EXAMPLE III A silver halide gelatin emulsion was prepared in the manner described in Example I without any diphenyldisulfidedicarboxylic acids and coated on a suitable acetate strip. Two-tenths percent of gelatin was prepared and 25 mg. diphenyldisulfide-3,3'-dicarboxylic acid was added to 1 liter of the 0.2% by weight gelatin solution. This gelatin solution was applied as a protective coating on top of the emulsion layer. A control light-sensitive element was prepared in the same manner using a gelatin top coat which did not contain the diphenyldisulfidedicarboxylic acids. The prints were then exposed to actinic radiation, developed in the developing composition utilized in Example I and ferrotyped. The prints prepared with the diphenyldisulfidedicarboxylic acids of this invention retained their black image color while prints prepared without diphenyldisulfide-3,3' dicarboxylic acid browned.

Essentially the same results were obtained utilizing 250 mg. of diphenyldisulfide-3,3'-dicarboxylic acid per liter of 0.2% by weight gelatin overcoating solution.

Variations and modifications can be made in the procedures, compositions and material without departing from the scope or spirit of this invention.

What is claimed is:

1. A light-sensitive silver halide emulsion containing as an antibronzing agent a compound selected from the group consisting of diphenyldisulfide-3,3'-dicarboxylic acid and diphenyldisulfide-4,4-dicarboxylic acid wherein said antibronzing agent comprises at least 0.5 gr. per mole of silver halide.

2. A light-senstive silver halide emulsion containing as an antibronzing agent at least 0.5 gr. of diphenyldisulfide-3,3'-dicarboxylic acid per mole of silver halide.

3. A light-senstive silver halide emulsion containing as an antibronzing agent at least 0.5 gr. of diphenyldisulfide-4,4'-dicarboxylic acid per mole of silver halide.

4. A light-sensitive photographic element comprising a base and a coating of a gelatin silver halide emulsion thereon, said emulsion containing as an antibronzing agent a compound selected from the group consisting of diphenyldisulfide-3,3'-dicarboxylic acid and diphenyldisulfide-4,4'-dicarboxylic acid wherein said antibronzing agent comprises at least 0.5 gr. per mole of silver halide.

5. A light-sensitive photographic element comprising a base and a coating of a gelatin silver halide emulsion thereon, said emulsion containing as an antibronzing agent at least 0.5 gr. of diphenyldisulfide-3,3'-dicarboxylic acid per mole of silver halide.

6. A light-sensitive photographic element comprising a base and a coating of a gelatin silver halide emulsion thereon, said emulsion containing as an antibronzing agent at least 0.5 gr. of diphenyldisulfide-4,4'-dicarboxylic acid per mole of silver halide.

7. A light-sensitive structure comprising a base, a layer of light-senstive silver halide emulsion thereon and an adjacent layer separate from the first mentioned layer containing as an antibronzing agent a compound selected from the group consisting of diphenyldisulfide-3,3-dicarboxylic acid and diphenyldisulfide-4,4'-dicarboxylic acid, wherein said compound is present in a concentration sufiicient to provide at least 0.5 gr. of antibronzing agent per mole of silver halide.

8. A process of forming photographic emulsions having reduced tendency to bronze which comprises forming an emulsion, ripening the emulsion and adding thereto an antibronzing agent selected from the group consisting of diphenyldisulfide-3,3'-dicarboxylic acid and diphenyldisulfide-4,4-dicarboxylic acid wherein said antibronzing compound comprises at least 0.5 gr. per mole of silver halide.

9. A process of forming a light-senstive photographic element having reduced bronzing tendency which comprises forming a silver halide emulsion, ripening the emulsion, coating said emulsion on a base and adding to the emulsion, just prior to the coating on the base, an antibronzing agent selected from the group consisting of diphenyldisulfide-3,3'-dicarboxylic acid and diphenyldisulfide-4,4'-dicarboxylic acid wherein said antibronzing agent comprises at least .05 gr. per mole of silver halide.

References Cited UNITED STATES PATENTS 3,226,232 12/1965 Dersch et al. 96-6l NORMAN G. TORCHIN, Primary Examiner.

J. R. EVERETT, Assistant Examiner. 

